An interior permanent magnet synchronous motor (IPM) is a motor having a layer of permanent magnet placed inside a rotor and primarily utilizing permanent magnet torque and utilizing auxiliary reluctance torque.
Resultant formula of the reluctance torque and the permanent magnet torque is as follows:T=mp(Lq−Ld)idiq+mpΨPMiq.
Wherein, T is an output torque of a motor, the performance of the motor can be improved by increasing the value of T; the first item in the equation following T is the reluctance torque, and the second item is the permanent magnet torque; ΨPM is the maximum value of stator-rotor coupling magnetic flux generated by a permanent magnet of the motor, m is a phase number of a conductor of a stator, Ld and Lq are inductances along axis d and axis q respectively, wherein axis d refers to an axis coincided with an axis of the main magnetic pole, and axis q refers to an axis perpendicular to the axis of the main magnetic pole, the perpendicular relationship refers to perpendicularity of electrical angles, and id and iq are components of an armature current in the directions of axis d and axis q respectively.
In the prior art, the performance of the motor is generally improved by improving the performance of the permanent magnet, that is, by increasing the permanent magnet torque to increase the value of the resultant torque so as to improve the efficiency of the motor, and the common method is to use rare-earth permanent magnets. However, since rare earth is a non-renewable resource and is expensive, the widespread use of this kind of motor is restricted. Additionally, the urgent demand of further improving the motor efficiency can not be met by only improving the performance of the permanent magnet.